A Markush, or generic structure, is a widely used convention in chemical and pharmaceutical patents. The flexibility and complexity of this format, however, preclude an easy understanding and analysis of chemical space. In this paper, an application package called MarVis (Markush Visualization) is introduced to help chemists visualize Markush structures in chemical patents. MarVis can output a report with the Markush structure showing the query substructure and also an R-group table of all the possible R-groups described in the patent. MarVis also has a unique interactive interface that allows chemists to explore and zoom in the chemical space to find a subset of interest. SMILES, with minimal extensions, was used to facilitate a variety of patent Markush structure studies.